Would it be possible to use a X2 on a 680i motherboard? If so, I think I know what my next card is.
If your going to use 2 x nVidia GPU's you could use that on the SLI board. If you want to use AMD GPU's you'd need a X-fire supported mobo to do that.
SLI (nVidia chipset) - means 2 GPU cards, or 2 slots on the mobo for 2 seperate video cards.
Tri-SLI (nVidia chipset) - means 3 GPU cards, or 3 slots on the mobo for 3 seperate video cards.
X-fire (AMD/ATI chipset) - means 2 GPU cards, or 2 slots on the mobo for 2 seperate video cards.
Spider platform (AMD/ATI chipset) - Rumor has it that it'll handle up to 4, IIRC, video cards, which means 4 GPU cards, or 4 slots on the mobo for 4 seperate video cards. Please correct me if I'm wrong on that, but that is what I remember reading somewhere.
Multicore GPU's on 1 card - is like having 1 video card with 2 GPU's on them, sorta like the nVidia 7950 gt had/has. I'm thinking that was your original question, but thought I show you the different variations out.